It’s not all black and white. This ubiquitous saying is quite appropriate to today’s subject, dynamic range.
Dynamic range is a term often bandied around in photographic articles and indeed there is a whole other discussion on creating high dynamic range. But what is it? What relevance does it have to you and your photography?
Well, quite a lot. It defines how your images look, their contrast, especially in scenes of high contrast. To newcomers, it can be a complicated and daunting subject so today we will try to explain it in layman terms.
What is Dynamic Range?
I am sure you have noticed that when you walk from a dark building into bright sunshine, your eyes can hurt with the sheer amount to light. If however you stood back from the door and looked out towards the bright light, your eyes will actually do a pretty good job of showing some detail in both the darkest and lightest areas. That's because our brains are pretty incredible at deciphering the information they receive from our eyes.
Now assuming you were standing in the same spot, let’s take a photograph of the same view through the door. No matter where you calculate the exposure, the image is going to be disappointing. The problem is that the sensors and processors on even the very best cameras of today, simply cannot deal with that much variation between the blackest black and whitest white.
Why is this? Well in layman’s terms digital cameras are computers. They work with data, with 0s and 1s and that comes with limitations. In simplistic terms that limitation is the amount of data that the sensor and processor are capable of working with.
If the dynamic range of the scene we are photographing contains more information than our cameras can deal with, then compromises must be made and we cannot record the full range of tones within that image.
So in answer to the question what is dynamic range? It's the number of stops of light that a camera can capture between pure black and pure white. Typically that will be between 9 and 14 stops on a modern camera.
So let's assume a scene with very high contrast such as the aforementioned door. If the exposure to get details in the shadows is 1/8th at f1.4 and the exposure for the brightest part of the image is 1/125th at f22, then we have around 14 stops of dynamic range. This means most cameras on the market today will have to either compromise the highlights, by blowing them out or the shadows by turning them pure black.
Sensors and Dynamic Range
Why do different cameras have different dynamic ranges? Well contrary to popular belief it's not actually about sensor size. It's about pixel size. The bigger the pixels the more light it can gather.
Think of a pixel as a light gathering bucket. Once it is full, it can't contain any more information. The sensor size comes into play because the bigger the sensor, the bigger the pixels can be on that sensor for a given megapixel count. The spacing between pixels is also important as the closer they are together the more they will interfere with each other electronically. This manifests itself as noise and can reduce the dynamic range.
When camera manufacturers quote the dynamic range of their sensors, they do so under perfect conditions. When we shoot, we are often not under the same conditions. Shooting Jpeg will reduce dynamic range as the camera applies corrections to the image such as contrast and saturation. Increasing ISO will also reduce the dynamic range of the sensor, quite significantly as you get to higher ISOs.
Improving Dynamic Range
While we cannot improve the dynamic range of our sensors, there are things we can do to control or improve the DR of the final images. The first it to shot RAW and low ISO. This means you are using close to the full potential of your sensor.
Secondly getting the exposure right will help your images, in particular avoiding clipped highlights. Understand the histogram and display clipped highlights on your LCD. Its easier to recover shadow areas a little than blown highlights.
Where you are struggling with dark foregrounds and bright skies, graduated neutral densities can be very useful. You can hold back the detail in the sky while exposing the foreground well.
Lastly don't be afraid of HDR, or High Dynamic Range photography. Yes, you can produce garish unnatural images, but with care and practice, you can also create beautiful very natural looking shots that far exceed the native dynamic range of your camera.
Dynamic range is an important subject. If we understand the limitations of our camera’s sensor we can overcome scenes with high contrast using some of the tools and techniques above.
For More On Dynamic Range
A Beginner’s Guide to Dynamic Range (Plus Useful HDR Photography Tips) – Dzvonko Petrovski takes us through some tips and tricks here at Light Stalking
Histograms: The Key To Perfect Exposure – Jason Row takes us through the use of histograms to ensure we get our exposure right
Fantastic Fundamental Light Skills – Photography Concentrate has a deal on their great mastering light course